Nonsinging amplifier



March 10. 1931. o. o. CECCARINE NONSINGING AMPLIFIER Filed Dec. 12, 1928 lNI/ENTOP 0. 0. C50 CAR/NI A TTO/PNE) Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE OLINDO O. CECGARINI, 015 LOS AN GEL-ES, CALIFORNIA, AS SIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK Application filed December 12, 1928.

It is well known that under certain conditions devices of the type mentioned produce oscillating currents in the circuits associated therewith which will interfere with the efficient transmission, reception, amplification and detection of signals when it is attempted to secure a high degree of amplification by using a plurality of devices connected in cascade.

A general object of the invention is to prevent singing or regeneration in high frequency amplifiersL 7 It is well known that the production of 05 cillations by such devices is due to coupling which is present between input and output circuits and that when a plurality of devices are connected in cascade a very small amount of coupling in a certain direction between the output circuit of the last device and the input circuit of a preceding device is sufiicient to start production of oscillations.

The prevention of singing due to the interelectrode capacity requires that the retroactive E. M. F. (or feed back) be zero at all 1 times or else in such phase relation with re- 30 spect to the input E. M. F. as to produce loss of amplification or degeneration.

Another object of the invention is to provide an amplifying system which Wlll be highly selective, that is, one which will give overcome electro-magnetic coupling between the circuits.

Another object of the invention is to eliminate the necessity for separately shielding the individual stages of the amplifier while at the same time placing the amplifier trans- Serial No.' 325,467.

formers close together so that they are within the stray magnetic fields of each other.

This is accomplished by placing the transformers of the adjacent stages with their cen ters in line and their axes mutually at right angles to each other and placing the transformers of alternate stages so that a magnetic coupling exists between them in a direction to oppose regenerative feed back.

Preferably an electrostatic shield is employed over the entire radio frequency amplifier. This shield has, however, no bearing on the regeneration action caused by the mutual coupling of alternate circuits. Without the use of an overall shield each transformer would actas an antenna and make volume control difficult, especially when the receiver is located in the proximity of a powerful radio transmitter.

The invention will be better understood by referring to the following description and accompanying drawing showing the pre ferred form of embodiment, representing a radio receiving circuit comprising three stages of radio frequency amplification, a detector, an audio amplifier and a loud speaker.

In the radio receiver represented by the drawing there are four radio frequency transformers 1, 2, 3 and 4 each associated with a tuning capacity 5, 6, 7 and 8. Three 3-element thermionic discharge devices 9, 10 and 11 are associated with the radio frequency transformers to act as radio-frequency amplifiers. The coils of each transformer are preferably of the single layer type. Transformers 1 and 3 are physically placed with their axes in line so that a magnetic coupling exists between them. Transformers 2 and 4: are phys ically placed with their axes in line so that a magnetic coupling exists between them and are so placed with respect to transformers l. and 3 that the centers of transformers 2 and 4 are in line with the centers of transformers 1 and 3 and the axes of transformers 1 and 3 are mutually at right angles with the axes 9 .to' them from a suitable source 15.

C C and C of space discharge devices 9, 10 and 11 are neutralized by currents in the opposite direction due to the magnetic potential resulting from the magnetic coupling between the transformers. lVith the connections made to accomplish this result the magnetic coupling between the transformers l and 3 and transformers 2 and 4 is in a direction to oppose regenerative feed-back. The distance between the axes of transformers 1 and 3 and between transformers 3 and i is adjusted so that the desired amount of degeneration clue to the magnetic coupling is obtained. This distance may be such that there will be a certain amount of regeneration, but not sufficient regeneration to cause singing, or the transformers may be placed so that regeneration is completely neutralized,

Plate potential is supplied to the thermionic discharge devices 9, 10 and 11 from a, suitable source 12 through the primary windings of transformers 2, 3 and 4. This potential is prevented from reaching the grids of thern'iionic discharge devices 10 and 11 by means of suitable blocking capacities 13 and la. Thev filaments of the thermionic discharge devices 9, 10 and 11 are connected in series and current is supplied Suitable grid potential ispreferably supplied to the thermionic discharge devices 9, 10 and 11. T iisis obtained for thermionic discharge de' vice 9 by the drop across resistance 16, for

thermionic discharge device 10 by the drop across the filament of thermionic discharge device 9, and for thermionic discharge 11 by the drop across the filament of thermionic discharge device 10. The methods shown of supplying filament current and plate and grid potential to the thermionic discharge devices forms no part of this invention and obviously other means well known to those skilled in the art can be employed. A suitable auteuna 1G is connected to transformer 1, a suitable detector 171 is connected to the output of thermionic discharge device 11, a suitable amplifier 18 to the output of the detector and a suitable receiver 19 to the output of. the amplifier.

Preferably a grounded electrostatic shi ld 20 is employed to shield the entire radio frequency amplifier. It may be constructed of any suitable material capable of preventing transformers 1, 2. 3 and 4 from acting as antennm. lVithout the use of such a shield volume control is diiiicult especially when the receiver is locatcdin the proximity of a powerful broadcasting station.

4 The operation of the amplifier system described above is as follows: Incoming high frequency signals are impressed on the grid filament circuit of thermionic discharge device 9 by means of the antenna 16 and high frequenev transformer 1 in the usual manner by adjusting the capacity 5 which tunes the circuit 521 to resonance with the signal. Capacities (3, 7 and 8 are also adjusted to tune the circuits 2e', 37, and 4r-8 to resonance with the incoming signals. The signals impressed on the grid-filament circuit of the thermionicdischarge device 9 are amplified by the discharge device and by means (if transformer 2 are impressed on the gridiiiament circuit of thermionic discharge device. 10. Since transformers 1 and 2 have their centers in line and their axes mutually at right angles to each other, no electro-magnetic coupling will exist between them. Due to the internal grid-plate capacity C of the thermionic discharge device 9, there will be an clectrosatic coupling between the input circuit and the output circuit which will tend to cause regeneration and singing. The signal voltage in the output circuit of thermionic discharge device 9 is amplified by transformer .2 and thermionic discharge device 10. The signal current in the output circuit of thernionic discharge device 10 induces a voltage across transformer 3 which is connected in the output circuit of this thermionic discharge device. Transformer 3 has been placed so that a magnetic coupling exists between it and transformer 1 in a direction to opposite "enerativc feed back. This coupling induces an elcctro-maguetic potential across transformer 1 which tends to produce a current .in transformer 1 in an opposite direction to that caused by the electro-static coupling through capacity G The action caused by. the magnetic coupling between the trans formers may be termed a degenerative action since it tends to reduce the signal and neutralize the currents caused by the regenerative action due to the internal capacity C Singing is thus prevented in thermionic discharge device 9. In a similar manner the magnetic coupling between transformers 4 and 2 induces an electromagnetic potential across transformer 2 which prevents singing in thermionic discharge device 10. This action may be continued in any number of stages in which the alternate stages lave their transformers magnetically coupled in a reverse direction.

lvhile a single embodiment of the invention has been shown and described in detail, it is understood that the invention is generic in character and is not to be considered as limited to the particular embodiment described since numerous modifications thereof may be made by persons skilled in the art without departing from the spirit of applicants invention, the scope of which is to be determined by the appended claims.

What is claimed 1. In a multi-stage amplifier including a thermionic discharge device in each stage, transformers coupling said discharge devices of adjacentstages, means for preventing undesired magnetic coupling between the transformers in adjacent stages, and means for creating magnetic coupling between the transformers in non-adjacent stages in a direction to oppose regeneration.

2. In a multi-stage radio frequency amplifier system, a plurality of thermionic discharge devices connected in tandem,'said discharge devices coupled by means of transformers, means for preventing undesired magnetic coupling between the transformers in adjacent stages, and means for creating magnetic coupling between the transformers in non-adjacent stages in a direction to oppose regeneration.

3. The method of balancing the inter-electrode capacity effects of vacuum tubes in a multi-stage transformer coupled radio frequency amplifier system which consists in creating magnetic coupling between said transformers in non-adjacent stages in a direction to oppose regeneration, and preventing magnetic coupling between said transformers in adjacent stages.

4;. In an amplifying system, a series of electric discharge devices connected in ms cade, each electric discharge device being provided with a tuned input circuit, and an output circuit, whereby inherent capacity coupling may exist, means for balancing out the retro-active E. M. F. due to said inherent capacity, said means comprising means for preventing electronnagnetic coupling be tween the input and output circuits of each of said electric discharge devices and means for creating magnetic coupling between the input circuit of each of said electric discharge devices and the output circuit of a subsequent electric discharge device in a direction to oppose regeneration.

5. A radio receiving circuit comprisingan antenna circuit, a plurality of three-element radio frequency amplifier tubes having plate, grid and filament and connected in cascade, each of said amplifier tubes having associated therewith an inductance, 'a variable capacity connected in effective shunt to said inductance to tune said inductance to resonance with a signal, a connection from said grid to one end of said'inductance, a connection from the other end of said inductance to said filament, a connection from the plate of each of said amplifier tubes to the inductance connected between the grid and filament of the following amplifier tube, said inductances positioned in space as to prevent electromagnetic coupling between the input and output circuits of each electron discharge amplifier tube and to produce electromagnetic coupling between the input circuit of each of said radio frequency amplifier tubes and the output circuit of a subsequent radio frequency amplifier tube in a direction to oppose regeneration.

6. An electrical network containing a plurality of thermionic amplifiers having. input and output circuits, each of said thermionic amplifiers having its input circuit adjustably coupled to the output olrcuit of a succeeding thermionic amplifier to oppose the effect upon said input circuit of currents in the p utput circuit of the same thermionic ampliier. i

7 vThe method of repeating and amplify-' ing substantially without distortion with a multi-stage ultra audio-frequency amplifier system having elements in the input circuit and elements in the output circuit of each stage which consists in creating magnetic coupling between at least one of the elements of each stage with at least one of the elements of a non-adjacent stage in a direction to oppose regeneration and preventing magnetic coupling between said input and output circuits of the same stage.

8. In a radio receiving system, an antenna circuit inductively coupled to the input circuit of a thermionic discharge device, said input circuit comprising an inductance and a capacitance tuned to resonance with a signal, a second inductance and capacitance coupled between the output circuit of said thermionic discharge device and the input of a second thermionic discharge'device to tune the input of said second thermionic discharge device to resonance with a signal, a third inductance and capacitance coupled between the output circuit of said last mentioned thermionic discharge device and the input of a third thermionic discharge device to tune the input of said third thermionic dischargedevice to resonance with a; signal, a fourth inductance and capacitance coupled between the output circuit of said last mentioned thermionic device and the input of a detector circuit, an amplifier circuit and a translating device, said inductances related to prevent electromagnetic coupling between the input and output circuits of each of said thermionic discharge devices and to create magnetic coupling between the input circuit of each of said thermionic discharge devices and the output circuit of a subsequent discharge device in a direction to oppose regeneration.

9. An amplifier for high frequency alternating currents comprising three-element amplifier tubes with tuned grid circuits in which the consecutive tubes are coupled together by transformers, said transformers having sufiiciently small magnetic coupling between the transformers connected to the input and output circuits of each individual tube and sufiiciently large coupling between transformers connected to the input of one tube and the output of a succeeding tube in a direction to oppose regeneration so that the effective inductive reaction of the grid circuit of a tube in the plate circuit of a preceding tube together with the inductive reaction of the plate circuit itself will always be below the critical Valuerequired to cause the preceding: tube to oscillate.

10. In a multi-stage ultra audio-frequency amplifier: system having elements capable of interaction; by their external magnetic fields, the method of repeating and amplifying substantially without distortion which comprises reducing to a less extent the interaction between-elements in alternate stages than the interaction between elements in adjacent stages.

11. Thecombinationin an amplifying'system of a plurality of electron discharge amplifiers each of which has an input and an output circuit, energy transforming means connecting the output circuit of each tube with the input circuit of a succeeding tube, means'for impressing currents which are to be amplified on the input circuit of one of said amplifiers and means for impressing energy variations produced in the output circuit of saidamplifier on the energy transforming means associated with said output circuit, the energy transforming means being so related as to prevent electromagnetic coupling between the input and output circuitsof each electron discharge amplifier and to produce electromagnetic coupling between the input circuit of each electron discharge amplifier and the output circuit of an electron discharge amplifier other than that to which said last mentioned input circuit is connectedin a direction to oppose regenera- 0 tion.

In witness whereof, I hereunto subscribe my'name this 4th day of December, 1928. OLINDO O. CECCARINI. 

